IPv6 Communication over Trunk Interfaces in Packet Tracer

[rc109]

Hello,

I’m encountering a challenge with IPv6 communication over trunk interfaces in Packet Tracer, specifically when using VLANs.

Context

In my lab setup, I’m using two Catalyst 3650 switches (simulated in Packet Tracer) connected via GigabitEthernet1/0/24 in trunk mode to allow multiple VLANs, with six VLANs currently authorized on the trunk link. I’ve configured IPv6 on each switch using SVIs (Switch Virtual Interfaces) for each VLAN. The goal is to establish IPv6 connectivity over the trunk using VLAN 10.

Issue

Despite the configuration appearing correct and testing across different setups, IPv6 communication fails between the two switches when trunk mode is enabled. IPv6 traffic over trunk links seems unsupported, as Neighbor Discovery (ND) messages (e.g., Router Advertisements) do not pass through, effectively preventing IPv6 connectivity. I’ve tried multiple approaches, including:

• Enabling ip routing to ensure Layer 3 routing capability.
• Configuring VLAN 10 as the native VLAN on the trunk to avoid tagging issues.
• Using sdm prefer dual-ipv4-and-ipv6 to optimize for IPv6, but this option seems unsupported in Packet Tracer.

Question

Has anyone successfully achieved IPv6 communication over trunk interfaces with VLANs in Packet Tracer? Is there a known workaround or specific configuration that would enable IPv6 Neighbor Discovery and other IPv6 traffic to function over a trunk in this simulated environment? Or is this indeed a limitation inherent to Packet Tracer?

Thank you in advance for any guidance or suggestions!

Best regards,

[Flavio Miranda]

@rc109 

 Can I see your PKT file?

Did you try something like

!

interface VlanX

no ip address

ipv6 address autoconfig

ipv6 enable

!

!

[rc109]

Hello, thank you for the response.

This is my first time posting here, so could you let me know how to share the .pkt file with you?

To provide more context, my VLANs are already communicating over IPv4. However, I have a web server that needs to be accessible via both IPv4 and IPv6.

Here’s an outline of my current configuration:

interface GigabitEthernet1/0/24
switchport access vlan 10
switchport trunk allowed vlan 10,20,30,40,50,60
switchport mode trunk
!
interface Vlan10
mac-address 00e0.f94e.5301
ip address 132.186.32.132 255.255.255.248
ipv6 address 2001:0:CAFE:10::2/64
!

On my second switch, the IPv6 address is configured as 2001:0:CAFE:10::1/64 for VLAN 10.

Is there any other information I can provide to help troubleshoot this issue?

[Flavio Miranda]

Please, zip your .pkt file and attach here so that I can take look

[rc109]

Here is the file, Thanks in advance for watching

ps: don't be afraid of the history, I'm a beginner on the subject ^^'

[Flavio Miranda]

Just tell me from where the web server is not ping. I can see that from the PC REUNION is possible to ping

[rc109]

Yes, I am trying to make these 2 switches (core and distributed) communicate in IPv6 on the gi1/0/24 interface

But I encounter the problem described in the subject

A the end, I will work so that the DNS server (at the top right) can reach the web server (the IPv6 on it currently is no longer the right one)

[Flavio Miranda]

Yeah, I dont believe this is supported. Not in packet tracer.

I will keep looking but I believe it will not support

[rc109]

Thanks for your feedback and the time you have spend on it !

I leave this subject open, if anyone ever knows of a workaround

[Devaa]

Hi @rc109 

It's purely IPv6 design and config issue. You document the IPv6 subnets in the GUI same as you did for IPv4 to get you a better picture. 

Here are the issues that I found and which I fixed. 

Issue 1: DNS server was unable to reach it's IPv6 gateway. Your default gateway should be R1. Keeping the distribution switch 1 as gateway got no use, but extra hop. However, IPv6 address in vlan 10 interface should be in X:Y:Z:5::/64 subnet, but you had it X:Y:Z:10::/64 (no use). Also in R1, IPv6 address should be configured in vlan 10 sub-interface, but you had it in the parent interface (native vlan 1). After configuring the R1 vlan 10 sub-interface with X:Y:Z:5::1/64, the DNS server was able to reach gateway. 

Issue 2: Your Web Server subnet X:Y:Z:2::/64 which is configured in R3 is also configured in R1 interface towards R2. So, technically Web server subnet is directly connected in R1. Hence, your packet will not even leave towards R3. I changed the subnet from X:Y:Z:2::/64 to X:Y:Z:6::/64 in link between R1 to R2. 

Issue 3: No proper IPv6 static route in R1 to reach X:Y:Z:2::/64 and R3 to X:Y:Z:5::/64. Instead you had a static IPv6 route in reverse which is your directly connected subnet itself. I also removed all static IPv6 routes and enabled IPv6 RIPng and advertised all the IPv6 subnets properly. 

You can see in the below screenshot, the DNS server is able to ping Web server over IPv6. I changed the IPv4 default gateway of DNS server as well, just to reduce one hop in routing. 

Find the attached ZIP file with fixed topology. 

Hope this helps.